1. Field of the Invention
This invention relates generally to rotary control valves such as ball valves or cylindrical plug valves. More particularly, the invention relates to such valves which are modified to reduce noise and vibration produced during partial closure of such valves.
2. Description of the Prior Art
The volumonous prior art of rotary control valves has searched for solutions to the problem of noise generation during throttling operation of such valves. U.S. Pat. No. 5,070,909 to Davenport tries to solve the problem by placing parallel conduits in entry and exit flow passages of the valve body and also placing similar conduits in the flow path of the ball valve in the valve body. Additionally, transverse holes between channels are provided in the ball valve.
U.S. Pat. No. 4,774,984 to Peters discloses a cylindrical plug valve with the plug having a flow passage through it dividing the plug into two halves. One half serves to close the flow passage of the valve when it is in a fully closed position. The other half has channels provided in it, such that when the valve is in a throttling position, fluid is partially directed through the channels in the plug element. Such channels are provided in the plug in an effort to decrease flashing and cavitation of the fluid through the valve so as to reduce noise.
U.S. Pat. No. 4,530,375 to Bey discloses an attenuating rotating valve in which the rotating closure member or valve element may be rotated from a fully closed position to a throttling position to a fully open position. A fixed attenuating element within the flow passage of the valve includes transverse channels in it through which fluid must pass when the valve is in a throttling position.
U.S. Pat. No. 4,364,415 to Polon discloses still another throttling ball valve in which the interior of the flow passage of the ball valve element includes longitudinal baffles which require fluid passing through the valve when it is in a throttling position to traverse a tortious back and forth longitudinal path to the valve exit passage.
All of the valves identified in this description of prior art are characterized by high cost in fabricating attenuation devices within the valve.
3. Identification of objects of the Invention
A primary object of this invention is to provide an improved rotary-control valve that is characterized by simplicity and low cost, yet is effective in reducing noise during throttling operation of the valve.